The spectral energy density (SED) method is used to obtain the phonon dispersion of materials in molecular dynamics codes, e.g., LAMMPS. We show how the electric analog of the SED method can be done using commercial circuit simulators to find the dispersion of periodic lossless LC circuits. The purpose of this article is (a) to demonstrate how SED proves useful, should the analytic methods of calculating dispersion of a circuit render difficult e.g., due to nonlinearity or having large number of elements in each unit-cell, and (b) to show how the concepts like Brillouin zone (BZ), dispersion (or band structure), zone folding, gap formation, and avoided crossing can be taught to students of electrical engineering by highlighting the analogies between phonons and periodic circuits. This analogy also suggests that thermal devices, e.g., heat rectifiers can be simulated and understood using commercial circuit simulators.